A system of this type is eg an audio system where a number of microphones or other transducers are connected to receiving equipment (eg mixing or measuring electronics) and where the operation of the microphones or electronics connected thereto is to be controlled during operation of the system. The operation to be controlled may be the direction characteristics of microphones or filtering or amplification taking place before or after A/D conversion of the measured signal. In this type of system, it will be desired that the controlling of the microphones or electronics connected thereto is performed from the site of eg the mixing electronics in order to be able to perform all actions from this site.
Another type of system wherein the present invention may be used is a system where signals are transferred from signal generating means to a signal receiving means and where power is to be supplied to the signal generating means.
In general, a number of problems may be encountered in systems where a large number of cables are required in order to interconnect the individual elements of the system.
If, eg, the system is one for measuring sound emitted by a car in a wind tunnel, a large number of sound measuring transducers are positioned in the car and in the wind tunnel in order to measure the sound emitted therefrom and in order to subsequently or simultaneously be able to exactly determine where in the car noise is generated.
Thus, a large number of transducers are to be connected to a common signal receiving and processing unit wherein the signals are intercorrelated in order to determine where in the car noise is generated.
In setups of this type, problems will easily occur during setting up, as cables to the individual transducers may accidentally be interchanged. Should this happen, the calculations performed in the processing step will produce erroneous results due to the fact that the sound pattern assumed by the calculations is not the factual sound pattern in the car.
The problem will be additionally increased, if the transducers are connected to pre-amplifiers and/or A/D converters which are to be controlled during the operation of the system. In this situation, cables will also be required for the controlling signals for the A/D converters.
A similar problem will be present, if the A/D converters or other signal sources require power from power sources. In this situation also power cables are to be provided in the system.
Having to provide additional cables will increase the probability of errors taking place. Finding and correcting an erroneously connected cable may be time and resource consuming and is in no way desired. In fact, even detecting that a problem exists is difficult.
Another advantage of providing a more simple cable having a smaller number of eg electrical or optical conductors is the fact that the connectors typically interconnecting the electronics and the cable may be made smaller and with a smaller weight. This provides the opportunity to provide less support for the connectors and eg to provide smaller boxes or the like for the electronics.
Providing eg three different cables to an acceleration transducer incorporating an A/D converter will put demands as to the size and strength of the transducer just in order to provide space for three connectors and in order to provide sufficient strength of the casing thereof so as to withstand assembly/disassembly of the connectors.
In addition, the fastening of the transducer to eg the car must be strong enough for holding the weight of the transducer, the connectors of the cables and part of the cables. Providing just a single cable may provide smaller transducers and reduced demands to the fastening and support therefore.
Furthermore, larger and heavier transducer casings may deteriorate the overall and directional sensitivity as well as the frequency response of the transducer. In general, the smaller the weight of certain types of transducers, the better the measuring characteristics thereof.
Thus, it is an object of the present invention to provide a system in which the number of cables or other signal transferring means may be reduced due to the fact that the cables may be used for more than a single purpose.
It is another object of the invention to enable existing setups comprising fixed or non-fixed cables to be used for more complex uses. In this manner, no additional cables need be provided.
A third object of the invention is that of providing a system in which the individual parts may have different dates of obsolescence in that the invention makes the date of obsolescence of eg cable setups at least more independent of that of the electronics communicating therethrough. Procuring electronics requiring additional cables will automatically make not only the old electronics but also the existing cable structure obsolete. This is avoided by the present invention.
A fourth object of the invention is providing a more simple setup as the identification of external units may be obtained through standard communication with these units--also during operation. Thus, pen&paper mapping of the system in order to prevent errors during setup is obviated. Subsequent to setting up the system, the actual setup may be obtained via the transmitting cables.
A fifth object may be seen in the audio field, where an especially critical situation may arise during eg concerts where a set of main microphones are used for measuring the overall sound of eg an orchestra and where a number of assisting microphones are used for measuring the sound of individual instruments or singers. Due to the main and assisting microphones having different distances to the instruments/singers, a filtering effect may be obtained in the combined signal. This problem may be solved by adding time delays at appropriate positions. However, these time delays should be determined within quite narrow tolerances in order to avoid the filtering effect. The system and method of the invention aids in this direction.
Systems using the same cables for more than one purpose have been suggested for a number of purposes.
Smart sensors have been suggested for use in a number of electrical appliances in homes in order to be able to control or at least monitor the operation of these appliances from a central console. In Electronic design, Sep. 18, 1995 "Where Will Smart Homes Get Their Smarts?", Clifford Meth, a system where these sensors are interconnected via the normal power lines of the home is described.
In this system, the sensors monitor the operation of the appliances and transmit information over the power lines to the console.
Another system wherein information is transmitted over cables used for transmitting additional information is described in a questionnaire issued by the Market Study Committee "IEEE TC-9/NIST Smart Transducer Interface Standard Information Gathering Project" in May 1995. In this questionnaire an interface standard is suggested between smart transducers and computer networks in order for transducer manufacturers to be able to manufacture transducers generally adaptable to computer networks.
The two above-mentioned systems are of a type where the information from different sensors is typically independent and where the actual timing between transmittal and receipt of the information is not crucial.
A third suggestion of using a two-connector interface for two-way data communication is the Universal Serial Bus Specification (See Universal Serial Bus Specification Revision 0.9 as issued by Compaq, DEC, IBM, Intel, Microsoft, NEC and Northern Telecom). This bus supports "real-time data for voice, audio, and compressed video" (See page 11, item 3.1). In addition, this bus furthermore supports additional data transported via the same two connectors. In this context, "real-time" means that a maximum latency of 1 ms is guaranteed from an external unit to the receiver.
However, due to this bus being adapted to internal communication in computers--typically multi media computers--the data transferred therethrough is packed in data blocks. In addition, this bus does not support cables longer than 5 meters. The limits to the latency and the cable length is set by the handshaking taking place in connection with the communication over this bus.
A different situation exists, if the timing between the signals transmitted from the signal generators, such as a number of transducers with pertaining A/D converters, is of importance to the system. In this situation, the above-mentioned systems would not suffice, as standard or even dedicated computer networks, which are normally used for transferring information from one site to the other, are not designed to guarantee that the information from two independent signal sources to a common receiver is timed in a given manner.
In typical computer networks, the information will be transmitted from transmitter to receiver, but the network does not guarantee when this transmission will take place. In addition, these networks do not detect any delays in transmission.
In eg stereo audio systems, the maximum acceptable time difference between receipt of the signals representing left and right channel is relatively small, as a too large time difference will be detectable as an erroneous phase of the combined signal. A 1 ms time difference will be detectable using the human ear and is not at all accepted in eg professional audio such as in sound studios.
The same applies to systems where a number of related signals 20 are measured by a number of eg transducers and which form the basis of a subsequent processing for deriving information about the means emitting the signals, such as in the above wind tunnel system. In these systems, the phase information of these signals is essential. This information may be lost if the system can not at all times fulfil strict timing requirements as to it being determinable whether the signals have been transmitted or measured with a given time difference.
Standard computer networks make an effort out of handling unforeseen stochastic events such as unplugging of parts thereof, turned off equipment, etc. This directly impedes the performance of these networks in the area of the present invention as timing in the networks is eliminated due to these factors.
These are the main reasons why networks similar to computer networks are not used nor contemplated for purposes where a more or less strict real time demand is posed to the system--that is, where the timing between signals from different sources matters. In this type of systems, separate, dedicated cables are typically used for transporting this information in order to ensure that the transmission is not interrupted. The very concept of computer networks is not directed to the solution of problems of this type.
A special aspect of the present type of system which cannot be solved by computer networks is the fact that the signal to be measured typically has to be detected in a manner providing much more data than may be packed into a normal data block in network communication. The timing of a standard computer network will deteriorate if more than a single block is required from the external units. This is due to the fact that timing between individual blocks is also not supported by standard networks.
Therefore, in this aspect the signals typically measured by the present type of system are measured in a manner so that the corresponding signals to be used in the system are transmitted to the receiving means in a more continuous manner. In this way, signals having virtually any time duration may be handled without limitation due to the transmission of the digital signals. However, this type of transmission puts the demands to the system as to the timing of the signals from different transducers.
Systems of this type may additionally be seen from U.S. Pat. Nos. 5,025,653 and 5,357,141, International applications with publication numbers WO 95/08759 and WO 85/05178 as well as in European patent applications with publication numbers EP-A-0 691 542 and EP-A-0 217 509. In EP-A-0 542 345, a system is disclosed wherein information is directed two-ways in a two-wire cable.